Method for the production of N-alkenyl-amides

ABSTRACT

A process for preparing N-alkenyl-amides by reacting the corresponding NH-amides with acetylenes in the liquid phase in the presence of basic alkali metal compounds and of a cocatalyst comprises using as the cocatalyst diols of the general formula (I)                    
     where X 
     is branched or unbranched alkylene selected from the group consisting of                    
     where R 1  to R 6  are independently hydrogen or C 1 - to C 4 -alkyl; 
     or 
     branched or unbranched cyclic alkylene of 3 to 14 carbon atoms including 3 to 12 ring carbon atoms, 
     their monoalkenyl ethers, their dialkenyl ethers or mixtures thereof.

This application is a 371 of PCT/EP001/12515, filed Dec. 11, 2000.

The present invention leads to an improved process for preparingN-alkenyl-amides by reacting the corresponding NH-amides with acetylenesin the liquid phase in the presence of basic alkali metal compounds anda cocatalyst.

N-Alkenyl-amides are used as monomers in the manufacture of plastics andpaints. Polyvinylamides are used for example as laundry detergentassistants, as auxiliaries in cosmetic and medical products and also forstabilizing and clarifying beers and fruit juices. Polyvinyl-lactams,especially polyvinylpyrrolidone polymers, are widely used, for exampleas dispersants for pigments, as laundry detergent assistants, asauxiliaries in cosmetic and medical products and also as auxiliaries intextile processing and adhesive technology.

N-Alkenyl-lactams are produced on an industrial scale by reacting thecorresponding NH-lactams with acetylenes in the presence of basiccatalysts (see W. Reppe et al., Justus Liebigs Ann. Chem., 601 (1956)page 135-8 and DE-Auslegeschrift 1 163 835).

DE-Offenlegungsschrift 3 215 093 discloses a process for vinylating2-pyrrolidone with ethyne in the presence of basic catalysts and in theadditional presence of a polyoxyalkylene compound as cocatalyst. Usefulpolyoxyalkylene compounds are said to be crown ethers (eg 18-crown-6),polyoxyethylene, polyoxypropylene, selectively capped by alkyl or phenylgroups. Conversions up to 63% and selectivities around 90% are reported,the corresponding yield being not more 57%. The formation of polymericresidues is reduced. However, the cocatalysts mentioned are costlymaterials which are generally not recoverable, since they have highboiling points and therefore remain in the distillation bottoms togetherwith the polymeric byproducts. In addition, they are not stable in thestrongly basic medium of the reaction.

U.S. Pat. No. 5,665,889 describes a method for the production ofN-vinyl-2-pyrrolidone from 2-pyrrolidone and ethyne in the presence ofbasic alkali metal compounds using cocatalysts comprising hydroxyend-capped ether oligomers, for example polytetrahydrofuran, or lineardiols having at least 4 carbon atoms, for example, 1,4-butanediol. Thevinylation takes place at a temperature ranging from 100 to 200° C., andat a pressure ranging from 7.5 to 30 atm (from 7.6 to 30 bar) in thecourse of a reaction time of several hours. The use of 1,4-butanediolproduced a yield of only 77.2% even after a reaction time of 4 hours.The present inventors have determined that these cocatalysts, which havehigh boiling points, are generally impossible to separate from thepolymeric byproducts or in the case of the use of 1,4-butanediol can beseparated from the product of value only by means of inconvenientdistillative or chemical methods.

It is an object of the present invention to develop a process forpreparing N-alkenyl-amides that does not have the recited disadvantages,that permits yields of more than 80% and that makes the pure productobtainable in a simple manner.

We have found that this object is achieved by a process for preparingN-alkenyl-amides by reacting the corresponding NH-amides with acetylenesin the liquid phase in the presence of basic alkali metal compounds andof a cocatalyst, which comprises using as the cocatalyst diols of thegeneral formula (I)

where X

is branched or unbranched alkylene selected from the group consisting of

where R₁ to R₆ are independently hydrogen or C₁- to C₄-alkyl;

or

branched or unbranched cyclic alkylene of 3 to 14 carbon atoms including3 to 12 ring carbon atoms,

their monoalkenyl ethers, their dialkenyl ethers or mixtures thereof.

The process of the invention provides a way of obtainingN-alkenyl-amides in high selectivity and high yield from thecorresponding NH-amides and acetylenes in the presence of basic alkalimetal compounds and of an inexpensive cocatalyst which is simple toremove again from the reaction mixture.

An essential aspect of the process according to the invention is thepresence of a cocatalyst (I)

where X is branched or unbranched alkylene selected from the groupconsisting of

where R₁ to R₆ are independently hydrogen or C₁- to C₄-alkyl,

or where X is branched or unbranched cyclic alkylene of 3 to 14 carbonatoms including 3 to 12 ring carbon atoms,

and/or its monoalkenyl ethers, its dialkenyl ethers or mixtures thereof.

Cocatalysts (I) useful in the process of the invention include forexample 1,2-ethanediol (monoethylene glycol), 1,2-propanediol,1,2-butanediol, 2,3-butanediol, 2-methyl-1,2-propanediol,1,2-pentanediol, 2,3-pentanediol, 2-methyl-2,3-butanediol,1,2-hexanediol, 1,3-propanediol, 1,3-butanediol,2-methyl-1,3-propanediol, 1,2-cyclopropanediol, 1,2-cyclobutanediol,1,3-cyclobutanediol, 1,2-cyclopentanediol, 1,3-cyclopentanediol,1,2-cyclohexanediol, 1,3-cyclohexanediol, 1,4-cyclohexanediol,1,2-cycloheptanediol, 1,3-cycloheptanediol, 1,4-cycloheptanediol,1,2-cyclooctanediol, 1,3-cyclooctanediol, 1,4-cyclooctanediol,1,5-cyclooctanediol, 2-hydroxymethyl-1-cyclopropanol,2-hydroxymethyl-1-cyclobutanol, 3-hydroxymethyl-1-cyclobutanol,2-hydroxymethyl-1-cyclopentanol, 3-hydroxymethyl-1-cyclopentanol,2-hydroxymethyl-1-cyclohexanol, 3-hydroxymethyl-1-cyclohexanol,4-hydroxymethyl-1-cyclohexanol, 2-hydroxymethyl-1-cycloheptanol,3-hydroxymethyl-1-cycloheptanediol, 4-hydroxymethyl-1-cycloheptanol,2-hydroxymethyl-1-cyclooctanol, 3-hydroxymethyl-1-cyclooctanol,4-hydroxymethyl-1-cyclooctanol, 5-hydroxymethyl-1-cyclooctanol,1,1-bis(hydroxymethyl)-cyclopropane,1,2-bis(hydroxymethyl)-cyclopropane, 1,1-bis(hydroxymethyl)-cyclobutane,1,2-bis(hydroxymethyl)-cyclobutane, 1,3-bis(hydroxymethyl)-cyclobutane,1,1-bis(hydroxymethyl)-cyclopentane,1,2-bis(hydroxymethyl)-cyclopentane,1,3-bis(hydroxymethyl)-cyclopentane, 1,1-bis(hydroxymethyl)-cyclohexane,1,2-bis(hydroxymethyl)-cyclohexane, 1,3-bis(hydroxymethyl)-cyclohexane,1,4-bis(hydroxymethyl)-cyclohexane, 1,1-bis(hydroxymethyl)-cycloheptane,1,2-bis(hydroxymethyl)-cycloheptane,1,3-bis(hydroxymethyl)-cycloheptane,1,4-bis(hydroxymethyl)-cycloheptane, 1,1-bis(hydroxymethyl)-cyclooctane,1,2-bis(hydroxymethyl)-cyclooctane, 1,3-bis(hydroxymethyl)-cyclooctane,1,4-bis(hydroxymethyl)-cyclooctane or1,5-bis(hydroxymethyl)-cyclooctane.

Preference is given to the use of cocatalysts of the formula (Ia)

where Y is linear alkylene (CH₂) a, where a is 0 or 1,

or where Y is cycloalkylene having 3 to 12 ring carbon atoms,

and/or their monoalkenyl ethers, their dialkenyl ethers or mixturesthereof.

Preferred cocatalysts (I) for the process of the invention include forexample 1,2-ethanediol (monoethylene glycol), 1,3-propanediol,1,1-bis(hydroxymethyl)-cyclopropane,1,2-bis(hydroxymethyl)-cyclopropane, 1,1-bis(hydroxymethyl)-cyclobutane,1,2-bis(hydroxymethyl)-cyclobutane, 1,3-bis(hydroxymethyl)-cyclobutane,1,1-bis(hydroxymethyl)-cyclopentane,1,2-bis(hydroxymethyl)-cyclopentane,1,3-bis(hydroxymethyl)-cyclopentane, 1,1-bis(hydroxymethyl)-cyclohexane,1,2-bis(hydroxymethyl)-cyclohexane, 1,3-bis(hydroxymethyl)-cyclohexane,1,4-bis(hydroxymethyl)-cyclohexane, 1,1-bis(hydroxymethyl)-cycloheptane,1,2-bis(hydroxymethyl)-cycloheptane,1,3-bis(hydroxymethyl)-cycloheptane,1,4-bis(hydroxymethyl)-cycloheptane, 1,1-bis(hydroxymethyl)-cyclooctane,1,2-bis(hydroxymethyl)-cyclooctane, 1,3-bis(hydroxymethyl)-cyclooctane,1,4-bis(hydroxymethyl)-cyclooctane or1,5-bis(hydroxymethyl)-cyclooctane.

Particular preference is given to the use of 1,2-ethanediol(monoethylene glycol), 1,3-propanediol and1,4-bis(hydroxymethyl)-cyclohexane and/or its monoalkenyl ether and/orits dialkenyl ether or mixtures thereof. Very particular preference isgiven to the use of 1,2-ethanediol (monoethylene glycol),1,4-bis(hydroxymethyl)-cyclohexane and/or its monoalkenyl ether and/orits dialkenyl ether or mixtures thereof.

Preferred alkenyl groups for the alkenyl ethers are branched andunbranched hydrocarbyl radicals having 2 to 6 carbon atoms and a doublebond. Particular preference is given to all those ethers which form insitu from the diols mentioned and the acetylenes added. Very particularpreference is given to the vinyl ethers (ethenyl ethers) and(1-methylethyl ethers), especially the vinyl ethers (ethyl ethers).

In a particularly preferred embodiment, the cocatalyst is added in itsdiolic form (I) to the reaction system and the corresponding mono-and/or dialkenyl ethers may be then be formed in situ.

Very particularly preferred cocatalysts accordingly include1,2-ethanediol and its 1-vinyloxy-2-ethanol and 1,2-divinyloxy-ethanevinyl ethers formed by the very particularly preferred reaction withethyne and also 1,4-bis(hydroxymethyl)-cyclohexane and its1-vinyloxymethyl-4-hydroxymethyl-cyclohexane and1,4-bis(vinyloxymethyl)-cyclohexane vinyl ethers formed by the veryparticularly preferred reaction with ethyne.

The cocatalysts to be used in the process of the invention are easy toremove from the reaction mixture, especially from the N-alkenyl-amideproducts of value, compared with prior art cocatalysts. The cocatalystused is easy to remove not only in its diolic form but especially alsoin the form of its reaction products. It is common knowledge thatalcohols can be alkenylated with acetylenes at elevated temperature andpressure in the liquid phase in the presence of basic catalysts. So thediolic cocatalysts to be used according to the invention will react withthe acetylenes during the NH-lactam alkenylation, but they certainly donot lose their positive effect. The alkenylation of the cocatalysts tobe used according to the invention is a consecutive reaction, wherefirst one OH group and then, if present, the other OH group isalkenylated. The reaction scheme is illustrated hereinbelow, althoughfor simplicity only the particularly preferred case of the alkenylationwith ethyne is illustrated. It will be appreciated that the alkenylationof the diols with acetylenes having more than 2 carbon atoms is likewisepossible. X is defined as described above.

Since the diolic cocatalyst (I) may also be completely converted,depending on the reaction conditions and the materials used, the boilingpoints of the mono- and dialkenylated compounds (II) and (III) inrelation to those of the N-alkenyl-amides to be prepared are of decisiveimportance. The greater the gap between these boiling points and thoseof the N-alkenyl-amides, whether in the direction of lower or higherboiling points, the simpler it is to remove the N-alkenyl-amidesprepared.

NH-amides useful as starting materials in the process of the inventioninclude cyclic and noncyclic amides which contain the “—CO—NH—” unit intheir charge-neutral form.

Useful noncyclic amides include for example the N-alkyl-amides ofbranched and unbranched, saturated and unsaturated C₁- to C₂₂-carboxylicacids, having branched and unbranched, saturated and unsaturated C₁- toC₁₀-alkyl groups on the amide nitrogen. Examples of noncyclic NH-amidesare the methyl-, ethyl-, propyl-, 1-methylethyl-, butyl-,1-methylpropyl-, 1,1-dimethylethyl-, pentyl-, hexyl, heptyl-, octyl-,nonyl- or decyl-amides of formic acid, acetic acid, propionic acid,butyric acid, valeric acid, isovaleric acid, pivalic acid, caproic acid,2-ethylbutyric acid, enanthic acid, caprylic acid, 2-ethylhexanic acid,pelargonic acid, isononanoic acid, capric acid, neodecanoic acid, lauricacid, myristic acid, palmitic acid, stearic acid, oleic acid, linoleicacid, linolenic acid, arachidic acid and behenic acid. Preferrednoncyclic NH-amides are N-methyl-acetamide, N-methyl-propionamide andN-ethyl-acetamide.

Particular preference is given to the use of cyclic NH-amides, which areknown as NH-lactams. Useful NH-lactams for the process of the inventioninclude 4- to 12-membered NH-lactams, for example 2-pyrrolidone,2-piperidone, ε-caprolactam and alkyl derivatives thereof, for example3-methyl-2-pyrrolidone, 4-methyl-2-pyrrolidone, 5-methyl-2-pyrrolidone,3-ethyl-2-pyrrolidone, 3-propyl-2-pyrrolidone, 3-butyl-2-pyrrolidone,3,3-dimethyl-2-pyrrolidone, 3,5-dimethyl-2-pyrrolidone,5,5-dimethyl-2-pyrrolidone, 3,3,5-trimethyl-2-pyrrolidone,5-methyl-5-ethyl-2-pyrrolidone, 3,4,5-trimethyl-2-pyrrolidone,3-methyl-2-piperidone, 4-methyl-2-piperidone, 5-methyl-2-piperidone,6-methyl-2-piperidone, 6-ethyl-2-piperidone, 3,5-dimethyl-2-piperidone,4,4-dimethyl-2-piperidone, 3-methyl-ε-caprolactam,4-methyl-ε-caprolactam, 5-methyl-ε-caprolactam, 6-methyl-ε-caprolactam,7-methyl-ε-caprolactam, 3-ethyl-ε-caprolactam, 3-propyl-ε-caprolactam,3-butyl-ε-caprolactam, 3,3-dimethyl-ε-caprolactam or7,7-dimethyl-ε-caprolactam.

Preference is given to using the unsubstituted 4- to 12-memberedNH-lactams

where n is from 2 to 10, for example β-propiolactam, 2-pyrrolidone(γ-butyrolactam), 2-piperidone (δ-valerolactam), ε-caprolactam and alsoalkyl-substituted derivatives thereof. Particular preference is given tothe use of 2-pyrrolidone (γ-butyrolactam), 2-piperidone (δ-valerolactam)and ε-caprolactam.

Acetylenes used in the process of the invention are preferablyunbranched and branched alkynes having 2 to 6 carbon atoms and aterminal triple bond, for example ethyne, propyne, 1-butyne, 1-pentyne,1-hexyne. Particular preference is given to the use of ethyne andpropyne, especially ethyne.

In the case of the very particularly preferred 1,2-ethanediolcocatalyst, for example, the boiling point of the divinylated1,2-dialkenyloxy-ethane is about 88° C. lower than that ofN-vinyl-2-pyrrolidone, obtainable in the process of the invention byreacting 2-pyrrolidone with ethyne. Similarly, the monovinylated1-vinyloxy-2-ethanol is significantly below the boiling point ofN-vinyl-2-pyrrolidone. In the case of the particularly preferred1,4-bis(hydroxymethyl)-cyclohexane, for example, the boiling point ofthe divinylated compound is about 38° C. above the boiling point ofN-vinyl-2-pyrrolidone, so that easy removal is possible in this casetoo. Both the low boiling cocatalyst systems to be used according to theinvention and the high boiling ones provide for easy removability of theN-alkenyl-lactam.

The cocatalyst to be used according to the invention is generally usedin an amount of from 0.1 to 10% by weight, based on the NH-amide used.An amount of from 0.5 to 5% by weight is particularly preferred.

The cocatalyst to be used according to the invention can be added notonly in its diolic form (I) but also in the form of its monoalkenylethers and dialkenyl ethers and mixtures thereof.

Basic alkali metal compounds useful as catalyst in the process of theinvention include the oxides, hydroxides and/or alkoxides of lithium,sodium, potassium, rubidium and/or cesium and also mixtures thereof.Preferred alkoxides are compounds of low molecular weight alcohols, forexample methoxide, ethoxide, propoxide, 1-methyl-ethoxide, butoxide,1-methyl-propoxide, 2-methyl-propoxide and 1,1-dimethyl-ethoxide.Preference is given to using the oxides, hydroxides and/or alkoxides ofsodium and/or potassium. Particular preference is given to sodiumhydroxide and potassium hydroxide. The basic alkali metal compounds maybe used as solids or solutions in water or alcohol. Preference is givento the use of solid, water- and alcohol-free alkali metal compounds.Mixtures of various alkali metal compounds are also possible.

The reaction with the acetylene may be carried out at a molar ratio offrom 0.02 to 6.0%, preferably from 0.05 to 4.0%, between the total ofbasic alkali metal compounds used and the NH-amide.

The process of the invention may be carried out as follows:

The first step of the process according to the invention may be todissolve the cocatalyst in the NH-amide. However, the addition may alsotake place later.

The next step is to contact the basic alkali metal compounds with theNH-amide. It may be pointed out that the NH-amide may at this pointalready include the requisite amount of cocatalyst. The alkali metalcompound is added, for example, by dissolving it in the liquid NH-amideor by adding a solution of the alkali metal compounds to the NH-amide.It is also possible to dilute the NH-amide, or the solution of thealkali metal compound in the NH-amide, with a suitable solvent, forexample in order to influence the reaction characteristics. Usefulsolvents dissolve both the NH-amide and the basic catalyst relativelyreadily and do not react chemically with the compounds used, ie have inparticular no acidic centers which would scavenge the basic groups, andthey are relatively easy to remove again, preferably by distillation,from the system after the synthesis of the N-alkenyl-amides. Examples ofuseful solvents are N-methylpyrrolidone, tetrahydrofuran or dialkylethers of glycols, di-, oligo- or polyglycols.

The solution of the basic alkali metal compounds in the NH-amide or itssolutions is generally prepared according to customary methods bycontacing the catalyst solid with the liquid by thorough mixing. Thisprovides an accelerated dissolution of the solid and counteracts anylocal heating due to the heat of dissolution. Suitable apparatuses areknown to those skilled in the art. Stirred tanks may be mentioned by wayof example without limitation. The liquid is charged initially and thecatalyst solid is added, if appropriate over a period of time,continuously or a little at a time with thorough mixing. When solutionsof the basic alkali metal compounds in water or alcohols are used, theprocedure is basically similar. Here too those skilled in the art wouldknow of suitable methods. It is also possible to add the cocatalysttogether with the alkali metal compound.

The solution of the basic alkali metal compounds in the NH-amide may beprepared not only in highly concentrated form as catalyst/NH-amide stocksolution but also in low-concentrated form as catalyst/NH-amide reactionsolution. The highly concentrated catalyst/NH-amide stock solution isset to a high catalyst concentration, which may be as high as thesolubility limit, while the low-concentrated catalyst/NH-amide reactionsolution is set to the catalyst concentration required for the reactionwith acetylene. It will be appreciated that all stages in between arepossible as well.

The reaction of the NH-amides with the alkali metal compounds byproduceswater or alcohols in an equilibrium reaction in liquid form. Water orthe alcohols formed remain in solution and, owing to the equilibriumrelation, prevent complete conversion between the NH-amide and the basicalkali metal compounds.

Specific removal of the water and/or alcohol of reaction formed resultsin a shift of the equilibrium in the direction of the alkali metal saltof the NH-amide, so that the salt mentioned may be obtained insufficient concentration. The addition of the basic alkali metalcompounds to the NH-amide may take place not only in a separate processstep but also during the removal of the water/alcohol of reaction. Inaddition, the cocatalyst may be added in a separate step after additionof the alkali metal compound or before or during the removal of thewater/alcohol of reaction.

The advantageous removal of the water and/or alcohol of reaction formedcontributes to obtaining a particularly high selectivity to and yield ofN-alkenyl-amides.

Particularly preferred methods for removing the water or low molecularweight alcohols of reaction are evaporation, binding to a suitable drier(adsorption) and removal through a suitable membrane. The methodsmentioned may even be employed when aqueous or alcoholic catalystsolutions are used.

Evaporation exploits the large difference in vapor pressure betweenwater/low molecular weight alcohol and the NH-amide. The water oralcohol of reaction is preferably evaporated at elevated temperaturebetween 50 and 150° C. and a reduced pressure between 0.1 kPa (1 mbarabs) and a subatmospheric pressure. Evaporation may be effected invarious ways. For example, it may be effected in a mixed vessel (egstirred tank) by heating and/or applying a reduced pressure. Similarly,stripping with an inert gas, for example nitrogen, is possible.Evaporation may also be effected by passing the solution through anevaporator. Such equipment is described in the pertinent technicalliterature (see for example Ullmann's Encyclopedia of IndustrialChemistry, 6^(th) edition, 1998 Electronic Release, Chapter“Evaporation”). A particularly preferred method of evaporation isdistillation. It may be carried out discontinuously, semicontinuously orcontinuously. In a discontinuous distillation, the NH-amide, thecatalyst, which may be completely or else only partially dissolved, and,if appropriate, the cocatalyst are initially charged to the distillationflask and the temperature is raised and/or the pressure reduced todistill off the water or alcohol of reaction. In a semicontinuousdistillation, for example, a solution of the catalyst in the NH-amide,which includes the cocatalyst, if appropriate, is fed to the column partand the water or alcohol of reaction is distilled off continuously. Thewater- or alcohol-free product collects in the distillation flask. Acontinuous distillation differs from a semicontinuous distillationmainly in that the water- or alcohol-free product is continuouslyremoved from the bottom region. The distillations are preferably carriedout at a pressure less than 0.1 MPa (1 bar abs).

The use of a drier exploits the exothermic adsorption of small moleculeson suitable solids having large surface areas. A particularly importantapplication is the removal of water. The technical literature describesa multiplicity of suitable driers (see for example Ullmann'sEncyclopedia of Industrial Chemistry, 6^(th) edition, 1998 ElectronicRelease, Chapter “Zeolites”). Useful driers include for example, withoutlimitation, zeolitic molecular sieves, for example the type 13X. Thedrying may also be effected in various ways. In one variant, forexample, the drier is disposed directly in the reaction system in whichthe later reaction with the acetylene takes place. In another variant,the solution is passed through a bed of the drier and only subsequentlyintroduced into the alkenylation reactor.

The third option mentioned, removal via a membrane, exploits the sizedifference between water or the low molecular weight alcohols and theteriary dialcohols. In one embodiment, the membrane is disposed directlyin the reaction system in which the later reaction with the acetylenetakes place. In another embodiment, the solution is passed over amembrane in an upstream apparatus. Suitable membranes are described inthe pertinent technical literature (see for example Ullmann'sEncyclopedia of Industrial Chemistry, 6^(th) edition, 1998 ElectronicRelease, Chapter “Membranes and Membrane Separation Processes”).

The water and/or alcohol of reaction is preferably removed by theabove-discussed methods of evaporation, adsorption and/or by a membrane.Any desired combinations between the individual methods are possible aswell and may even be advantageous. Without limitation there may bementioned a two-stage distillation, a distillation with downstreamadsorption or a removal by means of a membrane with downstreamadsorption. Particular preference is given to using distillativeremoval, which is most preferably carried out in a single stage, at apressure of less than 0.1 MPa (1 bar abs).

The water or alcohol of reaction is advantageously removed to a residuallevel of less than 1% by weight, preferably less than 0.5% by weight,particularly preferably less than 0.2% by weight, based on the totalamount of liquid.

The cocatalyst may also be added according to the invention after theremoval of the water or alcohol of reaction. Care must be taken toensure here that the cocatalyst feed is free of water and low molecularweight monoalcohols, for example methanol, ethanol or propanol, in orderthat the effect of the preceding stage is not diminished.

When the cocatalyst contains water or low molecular weight monoalcohols,these are to be removed before the cocatalyst is added. But in this caseit is preferable to add the cocatalyst to the NH-amide/catalyst solutionupstream of the process stage for removing the water or alcohol ofreaction.

The reaction with the acetylene is effected by contacting theabove-described, NH-amide-, catalyst- and cocatalyst-containing,beneficiated (ie water- and monoalcohol-free) solution with theacetylene in the liquid phase. The NH-amide/catalyst/cocatalyst solutionmay also have been diluted with a water- and monoalcohol-free solvent.Useful solvents generally include all solvents which are also useful inthe solution of the NH-amide and of the basic catalysts. Examples ofuseful solvents are N-methylpyrrolidone, tetrahydrofuran or dialkylethers of glycols, di-, oligo- or polyglycols. The reaction ispreferably carried out in undiluted form, ie without addition of afurther solvent.

If a catalyst/NH-amide solution was prepared with a catalystconcentration above the level required for the reaction with acetylene,for example a catalyst/NH-amide stock solution, and treated according tothe invention, it must now be diluted with further, water- andalcohol-free NH-amide. The diluting may take place both outside andinside the alkenylation reactor. The low-concentrated catalyst/NH-amidereaction solution treated according to the invention can be useddirectly.

The reaction with acetylene can be carried out in various ways. In thesemicontinuous process, the entire NH-amide/catalyst/cocatalyst solutionis initially charged and the acetylene metered in at the rate ofreaction. The product solution is normally not removed until after thereaction has ended. In the continuous process, theNH-amide/catalyst/cocatalyst solution and the acetylene are introducedcontinuously and the corresponding product solution is removedcontinuously.

The alkenylation is generally carried out at from 100 to 200° C.,preferably from 130 to 180° C., particularly preferably from 140 to 160°C. It is generally carried out at an acetylene pressure of less than 5MPa (50 bar abs), preferably less than 3 MPa (30 bar abs), mostpreferably less than 2.4 MPa (24 bar abs). However, the total pressureof the system may be significantly higher, since the gas atmosphereabove may for example additionally include inert gases, such as nitrogenor noble gases, which may be introduced by specific injection. So thetotal pressure in the system may easily be 20 MPa (200 bar abs) forexample. If relatively high molecular weight acetylenes are used, thenthe autogenous acetylene presure will be very low and may for example bedistinctly below 0.1 MPa (1 bar abs). Low molecular acetylenes, forexample ethyne, propyne and 1-butyne, are generally set to an acetylenepressure of greater than 0.1 MPa (1 bar abs). This provides aneconomical space-time yield. An alkenylation with ethyne as theacetylene is preferably carried out at an acetylene (ethyne) pressure offrom 0.5 to 3.0 MPa (5 to 30 bar abs), particularly preferably from 0.8to 2.4 MPa (8 to 24 bar abs), most preferably from 1.6 to 2.0 MPa (16 to20 bar abs).

The reactor used for the alkenylation may in principle be any apparatusdescribed for gas-liquid reactions in the pertinent technicalliterature. A high space-time yield requires thorough mixing between theNH-amide/catalyst/cocatalyst solution and the acetylene. Nonlimitingexamples are stirred tanks, stirred tank batteries, flow tubes(preferably with internal fitments), bubble columns and loop reactors.The reactor effluent is worked up according to known methods. Preferenceis given to a distillation into a plurality of fractions. Distillationsare preferably carried out at a pressure less than 0.1 MPa (1 bar abs).It is particularly preferable to recover not only the N-alkenyl-amidebut also the alkenylated cocatalysts as a fraction. Depending on thechoice of cocatalysts to be used according to the invention, thealkenylated cocatalysts are separated off in a lower boiling or higherboiling fraction before or after the N-alkenyl-amide. Various fractionsmay be mentioned without limitation: alkenylated cocatalyst (before orafter N-alkenyl-amide), N-alkenyl-amide, unconverted NH-amide, variousintermediate boilers, low boilers and high boilers. According tointention, these may be recovered as crude fraction or in high purity.It is also possible to combine some fractions. The distillation may becarried out continuously, semicontinuously or discontinuously. Inaddition, it may be carried out in one column, with or withoutsidestream takeoffs, as well as in a plurality of consecutive columns.Suitable methods will be known to those skilled in the art. The processof the invention, as described, is a simple way of obtainingN-alkenyl-amide in a purity of above 99.8%.

The optionally removed unconverted NH-amide may be recycled in theprocess of the invention without further purification measures. Forthis, it is not necessary to recover the starting material in highpurity, so that a crude-distilled fraction may be used as well. However,it is advantageous to remove those products having a distinctly higherboiling point.

The process of the invention allows the removed alkenylated cocatalysts(mono- and dialkenyl ethers of cocatalysts (I)) to be recycled. It isnot necessary to recover them in high purity, so that a crude-distilledfraction may be used as well. However, it is advantageous to removethose products having a distinctly higher boiling point. Any losses ofcocatalysts or their alkenylated compounds are to be made good byaddition of virgin, preferably diolic, cocatalysts.

The process of the invention is particularly preferable for preparing

and mixtures thereof. Starting materials for this are the correspondingNH-lactams 2-pyrrolidone (γ-butyrolactam), 2-piperidone (δ-valerolactam)and ε-caprolactam. The preparation of N-vinyl-2-pyrrolidone is veryparticularly preferred.

In a general embodiment, the basic alkali metal compound (catalyst) andthe cocatalyst are added a little at a time into the liquid, optionallysolvent-diluted, NH-amide and mixed in. The resulting solution is thenpassed over a zeolitic drier into a stirred tank. The presence of thedrier removes the water of reaction. The then almost anhydrous solutionhas the acetylene passed into it with thorough mixing at from 100 to200° C. The preferred ethyne is preferably introduced up to a pressureof 2.4 MPa (24 bar abs). Consumed acetylene is replenished. After theabsorption of acetylene has ceased, the reaction system isdepressurized. The reaction solution is transferred into a distillationcolumn and the N-alkenyl-amide is isolated overhead in high purity afterremoval of the lower boiling components.

In a further general embodiment, a mixing vessel is used to prepare analmost concentrated solution (ie about 80% of maximum solubility) of thebasic alkali metal compound in the NH-amide. This solution iscontinuously fed to a vacuum distillation column and the water ofreaction formed is taken off overhead. The water-free catalyst/NH-amidesolution is continuously removed from the bottom region and admixed withfurther anhydrous NH-amide and with anhydrous cocatalyst. The recyclingstreams are also fed in at this point. The reactant mixture is then fedinto a continuous loop reactor where the reaction with the acetylene iscarried out at from 100 to 200° C. The preferred ethyne is preferablyintroduced up to a pressure of 2.4 MPa (24 bar abs). The reactionsolution is continuously removed from the loop reactor and worked up bydistillation. The N-alkenyl-amide is isolated as pure product. Recovereduncoverted NH-amide and removed alkenylated cocatalyst are recycled.

In a third, particularly preferred embodiment, a mixing vessel is usedto prepare a solution of about 2% by weight of potassium hydroxide in2-pyrrolidone and admixed with about 1.0% by weight of 1,2-ethanediol.This solution is continuously fed to a vacuum distillation column andthe water of reaction formed is taken off overhead. The almost anhydroussolution is continuously removed from the bottom region into a stirredtank where the semicontinuous reaction takes place with the gaseousethyne at from 140 to 160° C. and from 1.5 to 2.0 MPa (15 bis 20 barabs). After the reaction has ended, the reactor contents are removedfrom the reactor into a distillative workup stage where they areseparated into low boilers, comprising l-vinyloxy-2-ethanol and1,2-divinyloxy-ethane, N-vinyl-2-pyrrolidone and high boilers. TheN-vinyl-2-pyrrolidone is recovered in high purity.

The process of the invention provides a simple way of obtainingN-alkenyl-amides in very high yield and purity by reacting thecorresponding NH-amides with acetylenes in the presence of basic alkalimetal compounds and of a cocatalyst. The outstanding advantages over theprior art are in particular:

The use of a cocatalyst which is, in the case of the particularlypreferred 1,2-ethanediol, very inexpensive.

The ease of removal of the N-alkenyl-lactam from the reaction solutionand the very high purity attainable thereby.

The possibility to recover and reuse the cocatalyst and its alkenylatedcompounds.

EXAMPLES

Definitions

The conversion, selectivity and yield reported in the description andthe examples are defined by the following equations:

Conversion=[m_(before)(NH-amide)−m_(after)(NH-amide)]/m_(before)(NH-amide)

Selectivity=m_(after)(N-alkenyl-amide)/[m_(before)(NH-amide)−m_(after)(NH-amide)]

Yield=Conversion×selectivity=m_(after)(N-alkenyl-amide)/m_(before)(NH-amide).

where:

m_(before)(NH-amide) is the mass of NH-amide used

m_(after)(NH-amide) is the unconverted mass of NH-amide

m_(after)(N-alkenyl-amide) is the mass of N-alkenyl-amide formed, afterpurifying distillation.

Procedure

The basic alkali metal compound was introduced into the liquid NH-amideand dissolved with stirring. The cocatalyst, if used, was added. Thenthe water of reaction was removed at 0.3 kPa (3 mbar abs) and 100° C.The almost anhydrous reaction batch was then introduced into anautoclave and pressurized with nitrogen to 0.2 MPa (2 bar abs) at roomtemperature. After heating to 150° C., ethyne was injected to 2.0 MPa(20 bar abs). Ethyne consumed by the reaction was replenished bycontinuous injection to 2.0 MPa (20 bar abs). After a predefined amountof ethyne had been taken up, the run was discontinued and the reactionproduct distilled. Analysis was by gas chromatography.

The amount of ethyne added is reported as the relative molar amountbased on the molar amount of NH-amide used.

Examples 1 to 4 Comparative Examples Without Cocatalyst

The above-described procedure was carried out in each case with 1040 gof 2-pyrrolidone being admixed with 12.48 g of KOH.

Relative Distillation Conver- Selec- Cocata- amount of residue siontivity Yield No. lyst acetylene [% by weight] [%] [%] [%] 1 — 0.51 4.251.0 93.7 47.8 2 — 0.58 4.3 65.2 91.7 59.8 3 — 0.79 6.5 83.6 86.4 72.3 4— 0.91 11.8 93.0 83.3 77.5

True, the conversion of NH-lactam increased with increasing reactiontime, but so did the formation of unwanted byproducts. This is evidentfrom the increase in the high molecular weight distillation residue.High conversion of NH-lactam, above the relative amount of ethyne added,is evidence for the increased formation of polymeric byproducts.

Example 5 Comparative Example Without Cocatalyst

The above-described procedure was carried out with 1060 g of2-pyrrolidone admixed with 13.46 g of KOH and 10.6 g of 1,4-butanediol.

Relative Distillation Conver- Selec- Cocata- amount of residue siontivity Yield No. lyst acetylene [% by weight] [%] [%] [%] 5 1,4- 0.917.6 89.0 91.2 81.2 Butane- diol

Distillative workup yielded N-vinyl-2-pyrrolidone in a purity of 99.1%by weight.

Example 6 Inventive

The above-described procedure was carried out with 1040 g of2-pyrrolidone admixed with 12.48 g of KOH and 10.4 g of 1,2-ethanediol.

Relative Distillation Conver- Selec- Cocata- amount of residue siontivity Yield No. lyst acetylene [% by weight] [%] [%] [%] 6 1,2- 0.917.3 88.8 90.3 80.2 Ethane- diol

Distillative workup yielded N-vinyl-2-pyrrolidone in a purity of >99.9%by weight.

Example 7 Inventive

The above-described procedure was carried out with 1040 g of2-pyrrolidone admixed with 12.48 g of KOH and 10.4 g of1,4-bis(hydroxymethyl)-cyclohexane.

Distillation Relative residue Conver- Selec- amount of [% by sion tivityYield No. Cocatalyst acetylene weight] [%] [%] [%] 7 1,4-Bis- 0.91 7.389.5 91.5 81.9 (hydroxy- methyl)- cyclohexane

Distillative workup yielded N-vinyl-2-pyrrolidone in a purity of >99.9%by weight.

A comparison of Examples 4 to 7, where the relative amount of ethyneadded was the same in each case, reveals the following picture:

The absence of a cocatalyst results in a high distillation residue of11.8% by weight being obtained at a yield of only 77.5%. All exampleswith cocatalyst show a distinctly higher yield between 80.2 and 81.9%combined with a comparatively low distillation residue fraction of 7.3and 7.6% by weight. Use of the cocatalyst to be used according to theinvention provides for distinctly better removability of theN-vinyl-2-pyrrolidone compared with the prior art. This shows itself ina measurably higher purity of >99.9% by weight compared with 99.1% byweight for the N-vinyl-2-pyrrolidone from the same distillative workup.

The cocatalysts to be used according to the invention are accordingly atleast equivalent in terms of yield and byproduct formation to those ofthe prior art, but significantly superior with regard to economy, easeof separation from the reaction solution and the purity attainable forthe N-alkenyl-lactam.

We claim:
 1. A process for preparing N-alkenyl-amides by reacting thecorresponding NH-amides with acetylenes in the liquid phase in thepresence of basic alkali metal compounds and of a cocatalyst, whichcomprises using as the cocatalyst diols of the general formula (I)

where Y is linear alkylene (CH₂)_(a), where a is 0 or 1; orcycloalkylene having 3 to 12 ring carbon atoms, their monoalkenylethers, their dialkenyl ethers or mixtures thereof.
 2. A process asclaimed in claim 1, wherein cocatalyst (I) is 1,2-ethanediol, itsmonoalkenyl ethers, its dialkenyl ethers or mixtures thereof.
 3. Aprocess as claimed in claim 1, wherein cocatalyst (I) is1,4-bis-(hydroxymethyl)-cyclohexane, its monoalkenyl ethers, itsdialkenyl ethers or mixtures thereof.
 4. A process as claimed in claim1, wherein said cocatalyst (I) is used in an amount of from 0.1 to 10%by weight, based on the NH-amide used.
 5. A process as claimed in claim1, wherein the basic alkali metal compounds used are sodium hydroxideand/or potassium hydroxide.
 6. A process as claimed in claim 1, whereinthe basic alkali metal compounds are used in a molar amount of from 0.05to 4.0% of the molar amount of the NH-amide used.
 7. A process asclaimed in claim 1, wherein the water and/or alcohol of reaction formedin the course of the reaction between the basic alkali metal compoundsand the NH-amide is removed from the system by evaporation, byadsorption and/or by a membrane.
 8. A process as claimed in claim 1,wherein the water and/or alcohol of reaction formed is removed from thesystem by distillation.
 9. A process as claimed in claim 1, wherein thereaction between the NH-amides and the acetylenes is carried out at from100 to 200° C. and at an acetylene pressure of less than 5 MPa.
 10. Aprocess as claimed in claim 1, wherein the cocatalyst, its monoalkenylether, its dialkenyl ether or mixture thereof is recovered and reused ascocatalyst.
 11. A process as claimed in claim 1, wherein theN-alkenyl-amides prepared are N-alkenyl-lactams.
 12. A process asclaimed in claim 11, wherein the N-alkenyl-lactams prepared areN-vinyl-2-pyrrolidone, N-vinyl-2-piperidone and/orN-vinyl-ε-caprolactam.